Reliability Analysis for Unrepairable Automotive Components

The analysis of the reliability parameters of a technical object and the determination of the change in the reliability of the object over time, requires the knowledge of the functional characteristics and reliability parameters of the elements included in a system. On the basis of the failure data of the selected element of the object, in this case the vehicle, it is possible to determine the average working time to failure of the element and the appropriate form of distribution that characterizes the reliability and durability parameters of the tested element. The main purpose of the research presented in the article was to develop a method of assessing the reliability of an electronic component of a vehicle-a boot lid contactor. This paper also presents three possible methods of repairing the boot lid contactor (sealing the housing with adhesive with better way, replacing the element with a new one or the most time-consuming solution, changing the shape of the boot lid). The authors also decided to determine the reliability and cost parameters that will allow preventive replacement of this element. The tests were carried out on a fleet of 61 vehicles of the same model, but with different body structures. Contactor failures were reported in 41 cases, of which 29 were in the hatchback construction and 12 in the estate type. The analysis of the distribution selection for the tested part of the passenger car-the boot lid contactor-was performed using the Likelihood Value (LKV) test to determine the rank of distributions. Also the maximum likelihood (MLE) method was used to estimate the distribution parameters. The three-parameter Weibull distribution was the best-fitted distribution in both cases. It was clearly defined that one model of car with two different types of body have vastly different reliability characteristic. Based on the reliability characteristic and parameters, the appropriate preventive actions can be taken, minimizing the risk of damage, thus avoiding financial losses and guaranteeing an appropriate level of vehicle safety.

Account of the errors of switching device for a system with 2-out-of-3 redundancy

The mathematical reliability model is developed that takes into account the errors of the first and second type of switching device for a system with 2-out-of-3 redundancy. The proposed model is designed to determine the reliability characteristic. The system consists of three identical energy sources and two switching devices. It is assumed that the system is the non-renewable and the switching devices cannot return to their original state. A fault tree mathematically describes the reliability of the system in which the logical conditions for the mutual influence of the components of the system and switching devices are specified. At the first stage, the fault tree is constructed for the system with ideal switching devices, e. g. they operate instantly and do not allow errors. At the second stage, the features of creating a dynamic k-terminal fault tree are considered taking into account the errors of the first and second kind. It is shown that to describe the system it is necessary to take into account six dynamic phenomena. Based on the fault trees, Markov models for the systems are constructed. Using this model, it is analyzed how the errors of the first and second type of switching devices influence the reliability characteristic of the system.

OPERATIONAL SOFTWARE PERFORMABILITY EVALUATION BASED ON MARKOVIAN RELIABILITY GROWTH MODEL WITH SYSTEMABILITY

In this paper, we discuss the operational performability evaluation model for the software-based system, introducing the concept of systemability which is defined as the reliability characteristic subject to the uncertainty of the field environment. Assuming that the software system can process the multiple tasks simultaneously and that the arrival process of the tasks follows a nonhomogeneous Poisson process, we analyze the distribution of the number of tasks whose processes can be completed within the processing time limit with the infinite-server queuing theory. Here we take the position that the software reliability characteristic in the testing phase is originally different from that in the operation phase. Then, the software failure-occurrence phenomenon in the operation phase is described with the Markovian software reliability model with systemability, i.e., we consider the randomness of the environmental factor which is introduced to bridge the gap between the software failure-occurrence characteristics during the testing and the operation phases. We derive several software performability measures considering the real-time property; these are given as the functions of time and the number of debugging activities. Finally, we illustrate several numerical examples of the measures to investigate the impact of consideration of systemability on the system performability evaluation.